1. Field of the Invention
This invention relates to the field of animal housing, and most advantageously to the housing of laboratory animals requiring isolation from contagion or isolation of contagion, using individually removable animal cage units.
2. Description of the Prior Art
In the art of housing animals, multi-compartment caging systems are employed for a variety of applications. These applications range from pet stores to demanding laboratory experimentation. Efficient use of space requires a compact living area and close storage of compartments. Problems that develop when confining a large number of animals in close proximity with one another include unpleasant odors, allergic reactions, inadequate air supply, cross-infection and difficulty with installation, removal and servicing of individual cage units.
In laboratory experimentation applications, animals are divided into a subject group and a control group, the subject group receiving a treatment under investigation while the control group is spared. When the subject group in an experiment is subjected to disease organisms, valid experimental results demand that the control group have absolutely no exposure to the disease in question. Even in situations not concerned with pathological diseases, completely pathogen-free animals are often required to reflect experimental results unaffected by stray pathogens. Multiple generations of animals having never been exposed to diseases, even through their ancestors, are therefore commonly bred. Production of such ultra-pure animals requires the ultimate in isolation.
Housing a large number of animals with even minimal degrees of isolation poses problems in supplying animals with basic needs such as air and food, as well as the problem of infection. In some prior art systems, banks of animal units have been individually fitted with pipe connections to supply and exhaust air, and sometimes to flush refuse from the animal housing unit. When a large number of animal units are mounted in a relatively small space, this maze of individual connections can be a nightmare for the person servicing the animals. This problem is only partially solved in systems that employ press-fit tube connections. On insertion of an animal unit into a system employing press-fit connections, the installer must visually line up the receptacle in the animal unit with the pipe in the rear of the mounting rack before the cage can be put in its final position. Inexact lineup of cages wastes supply air, may introduce pathogens, and may release contagion-bearing exhaust air. The complexity and inconvenience of individually piped systems therefore generates a substantial expense upon purchase and with continuing use.
In less demanding applications where some cross-ventilation can be tolerated, former animal housing systems have employed laminar flow ventilation. In laminar flow ventilation systems, a flow of air is supplied via a plenum over an entire bank of animal units having open tops. Theoretically, in such a system all the portions of cage ventilation air move parallel to all the other portions, out of the plenum and across the animal units. It is intended that each cage unit receive air directly from the plenum, and discharge air back into the flowpath without cross-ventilation to or from other units. Practically, the laminar flow ventilation method is not particularly effective at eliminating cross-ventilation. Discontinuities in the path of the air mass, including the animal compartments, generate eddy currents which preclude uniform air motion. Eddy currents and surface currents produce random swirling movements of air, sometimes directly opposite the movement of the larger directed air mass. This phenomenon is analogous to the way a canoeist can be more easily carried up river by staying close to the river bank.
Laminar air flow systems are usually designed to exhaust directly into the room. Persons allergic to the dander of laboratory animals, and all persons in installations where communicable disease experiments are carried out, must be equipped with personal protective equipment. If a plenum is used both on the air supply side and on the exhaust side, the animals will be enclosed and unobservable, and insertion and removal of animal units will be extremely inconvenient.
U.S. Pat. Nos. 4,249,842-Harr and 4,085,705-Gland et al attempt solutions to the cage ventilation problem using racks having hollow shelves comprising integral air ducts. The open-top cages are slideably suspended below the shelves on flanges. Openings in the shelves connect the air supply and/or exhaust to the inside of the animal compartment. While an advance over laminar flow systems, these systems are relatively open as no provision is made for seals or for closing cages upon removal.
It will be appreciated that problems with cross-ventilation and problems with convenience of installation and removal often involve a trade-off. If a system is completely airtight, installation and removal are likely to be inconvenient, requiring connection or disconnection of some sort of coupling. Conversely, a system which features convenience of installation and removal will generally do so at the expense of dependable, airtight couplings. The present invention seeks to provide a high performance airtight ventilation system that is nevertheless as convenient as a laminar flow system in ease of installation and removal of individual cage units.
The present invention provides a system whereby the cross-ventilation advantages of an individually-piped system are obtained, as well as the installation and removal convenience of a one-sided laminar flow system. In addition, the cage and/or the ventilation system are automatically sealed off when a cage is withdrawn. Each cage is therefore isolated at all times.
The system is widely applicable due to inexpensive yet sturdy and dependable construction. In simple embodiment, it is useful in pet stores and non-demamding laboratory work. In a strongly constructed unit, it is useful as a portable environment for shipping animals. In the most demanding laboratory contagious disease experiments, the full panoply of sealed cages and valves can be used. The total system can be employed to produce pathogen-free animals or to conduct communicable disease experiments, in addition to merely housing and transporting animals.